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thank Dr. Janine LoBello, St. Joseph’s Hospital & Medical Center in Phoenix, Arizona (USA), for contributing this case. We invite you to contribute a
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Case
of the Week #42

Clinical
history

The
patient is a 63 year old man who presented with a slowly enlarging, somewhat
painful mass of the cheek. A 6.0 x 4.5 x 3.0 cm portion of soft tissue was
received fresh for frozen section, which demonstrated a 2.4 x 1.0 x 0.4 cm well
circumscribed bright yellow to dark brown and hemorrhagic mass.

Although
acinic cell carcinomas represent only 2-6% of salivary gland tumors, they are
the third most common epithelial malignancy after mucoepidermoid carcinoma and
adenocarcinoma NOS, and represent about 10% of all malignant salivary gland
tumors. Most of these tumors occur in the parotid gland, with the remainder usually
in parotid lymph nodes, the submandibular gland or minor salivary glands. The
mean patient age is 44 years, but they are the second most common salivary
gland malignancy in children, after mucoepidermoid carcinoma.

Grossly,
acinic cell carcinomas are often encapsulated, tan-gray, and usually 3 cm or
less. Up to 3% are bilateral or multicentric. There is usually a mixture of
patterns, including solid, microcystic, papillary-cystic and follicular. However,
the lobular pattern of the normal parotid gland is absent. At least a portion
of the tumor demonstrates serous type acinar differentiation with large
polygonal cells containing granular, PAS+ basophilic cytoplasm due to zymogen
granules. The nuclei are eccentric, dark and round. There may also be clear
cells containing glycogen, vacuolated cells, glandular cells and intercalated
duct type cells. Lymphoid stroma may be present (Hum
Pathol 1997;28:595), as in this
case (image4).
Psammoma bodies are occasionally found. The striated ducts of the normal
parotid gland are lacking.

These
tumors may have amylase positive cytoplasm, although immunohistochemistry is typically
not helpful in diagnosis. Electron microscopy may demonstrate relatively
specific, zymogen like cytoplasmic granules that are electron-dense, round-oval
and membrane bound. The acinar tumor cells also have a well-developed rough
endoplasmic reticulum similar to normal salivary glands (see figure
5; zymogen granules-pancreas).

The
differential diagnosis may include normal parotid gland, which has a lobular
architecture with striated and interlobular ducts, as well as acinar cells.
The follicular and papillary patterns may resemble thyroid carcinoma and the
papillary pattern may resemble low grade salivary duct carcinoma (Am
J Surg Pathol 2004;28:1040). Fine needle aspirations must be interpreted with caution,
as they are often diagnosed as benign or non-neoplastic (Curr
Opin Otolaryngol Head Neck Surg 2006;14:62).

Behavior is difficult to predict from histology. However, there
is some general agreement on poor prognostic factors, many present in this
case. They include

Approximately
10-15% of acinic cell carcinomas metastasize, usually to local lymph nodes.
Adequate excision is important, as it reduces the recurrence rate from 80-90% (with
inadequate excision) to 10-30%. The surgeon can usually spare the facial nerve
(Ear Nose Throat J 2005;84:597).
Radiation therapy may be useful for positive surgical margins, advanced stage
or high grade histology. Overall 5 year survival is 90%, the highest among
parotid gland malignancies (Am
J Otolaryngol 2005;26:39), but
late deaths also occur.